Abstract: The paper reports on a study conducted in Maqu County located in eastern Tibet Plateau from 1982 to 2005. It was focused on the change of NDVI, climate factors and carrying capacity and their correlation, as well as the time lag effect between NDVI and temperature and precipitation. The correlation coefficients between NDVI and temperature and precipitation over the same period and the effect of including data from a prior period were analyzed under 16 combinations of temperature or precipitation (4 time durations by 4 time lags). The annucal changes of NDVI in spring and summer were significantly increased and their increasing range were 0.019/10 a and 0.022/10 a respectively. The annual change of seasonal and annual temperature as well as annual accumulated temperature above 0℃ were significantly increased over the study period and their increasing range were 0.5-0.7℃,0.6℃ and 121.5℃ respectively. The changes of seasonal and annual precipitation were not significantly different. The change of temperature in summer was steady but in spring and autumn it was variable. So too was the change of precipitation in four seasons. The correlation of monthly NDVI all the year round and the NDVI in spring and autumn in response to temperature at same period were significant positive or negative, and the value of correlation coefficient were 0.84, 0.77, -0.52 and 0.80 respectively. The correlation of average monthly NDVI every year in response to annual accumulated temperature above 0℃ and carrying capacity were significant positive, and the value of correlation coefficient were 0.66 and 0.45 respectively. The correlation of NDVI in response to precipitation in the current month and accumulated precipitation in two months prior (time durations: three months) were highly significant, the temperature in the current month and one month prior (time durations: two months) was also highly significant. By taking lag times into account we found significantly high correlations with the NDVI increase during the growing seasons. The increase of temperature in early growth stage (April) promoted vegetation growth. Generally precipitation later in the year had negative effects especially rains late in the growth stage of forage plants (August to September) as did high temperature at this time.